I wanted to understand why 100s of our users didn't come back after a 2 week product trial. Email was the best option, and in order to get a high response rate, each email should seem personalized, authentic, hand written, and to the point. Mailchimp/Sendgrid/etc was not an option for us.

Other tools were clunky, old, and slow - so I built Bulky. Easily create a Google Sheet of contacts (e.g. export from your DB), and import into Gmail using Bulky.